This invention relates generally to gas handling in industrial processes and more particularly to compression of gases which are subject to thermal or catalyzed decomposition, such as ozone.
Compression of gases generates heat of compression which goes to increase the temperature of the gas. Often this heat is removed from the compressed gas by passing it through an aftercooler which exchanges the heat with a reservoir of cool or refrigerated medium. Some gases are unstable and decompose due to the temperature increase attendant upon compression.
Ozone gas is used in many industrial processes. It is produced in ozone generators from air or oxygen in concentrations of up to about 15% by weight of ozone in air or oxygen carrier gas. Ozone generators normally produce ozone at less than about 15 psig in order to minimize capital costs for the generation equipment and to maintain high ozone generation efficiency.
Low pressure ozone is suitable for many processes, but many modern technologies require ozone at higher pressures. Also, many technologies require ozone at high concentrations in a variety of compatible carrier gases such as air, nitrogen, or oxygen.
Compression of ozone by commonly available reciprocating compressors or centrifugal compressors results in adiabatic heating and consequent thermal decomposition of a fraction of the ozone. By cooling the working parts of such compressors, or by providing intercoolers between stages, and aftercoolers for the compressed gas, most of the thermal decomposition can be avoided. However, such measures greatly increase the cost of such compressors; and half-measures still result in too great a loss of ozone to be acceptable.
One example of a technology which requires compressed ozone is bleaching of wood pulp at consistencies lower than about 45%. A typical system for bleaching low to medium consistency, i.e., up to about 18% consistency, may require an ozone pressure of between 30 and 200 psig for effectively contacting the ozone with the pulp or for effectively dissolving the ozone in a pulp bearing fluid. It is to be expected that an increasing number of processes will be and have been developed in a wide variety of technical fields which will require compressed ozone containing gases.
A liquid ring compressor may be used for compression of thermally reactive gas. Such compressors employ a liquid to act as an internal sealant between the casing of the compressor and the rotating vanes. The liquid forms a ring, by centrifugal action, against the compression chamber wall; and, by alternately filling and emptying the spaces between the vanes of the radially offset impeller, the liquid ring also serves as the compressant for the gas being compressed. Heat of compression is quite readily transferred from the gas to the liquid permitting the liquid ring compressor to approximate isothermal operation. This suppresses the thermal decomposition of the compressed gas and causes a corresponding increase in vapor pressure of the liquid ring. A quantity of the liquid may be discharged with the compressed gas and must be replenished for continuing operation.
In the case of ozone and some other gases, suppression of thermal decomposition is not alone sufficient to preserve the compressed ozone. Since ozone is very reactive, it is also subject to consumption and decomposition by reaction with the liquid of the liquid ring. Ozone even reacts with water in a variety of reactions which are well documented. One article dealing with these reactions is Weiss, J., "Reaction of Ozone With Water", Transactions of the Faraday Society, 31, 668 (1935), which is incorporated herein by reference.
Since ozone is a costly gaseous reagent, any measurable loss is to be avoided. Thus, with an ever increasing technological demand for high pressure ozone, the need for a non-destructive compression process becomes more urgent.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.